Theoretical study of prebiotic precursors: the peptide bond and its silicon, sulphur and phosphorous analogues

Details Theoretical study of prebiotic precursors: the peptide bond and its silicon, sulphur and phosphorous analogues Theoretical study of prebiotic precursors: the peptide bond and its silicon, sulphur and phosphorous analogues

Apr 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005ijasb...4..125c&link_type=abstract

International Journal of Astrobiology, vol. 4, Issue 2, p.125-133

Biology

1

Chon Systems, Chop Systems, Chsn Systems, Exobiology, Infrared Spectra, Peptide Bond, Quantum Chemistry, Rotational Constants, Sihon Systems.

Scientific paper

This paper looks at the possibility that the peptide bond may be more common than originally thought, leading to molecules of prebiotic interest containing heavier atoms of the second row of the periodic table. Ab initio Möller-Plesset (MP2) coupled-cluster molecular orbital methods and density functional theory have been used. A first investigation of the six-atom system [C,3H,O,N] showed that formamide, NH2[bond]CH[double bond]O, is the most stable system that can be formed. Systematic studies on this same system in which C, O and N were respectively replaced by Si, S and P were then carried out. It has been found that the peptide-like linkage is the most stable for [C,3H,S,N] and [Si,3H,O,N] where NH2[bond]CH[double bond]S and NH2[bond]SiH[double bond]O are about 10-14 kcal mol[minus sign]1 more favourable than the corresponding enol tautomers and well below other isomers on the energy scale. For [C,3H,O,P], the most stable species is CH3[bond]P[double bond]O, which is found 18 kcal mol[minus sign]1 below the PH2[bond]CH[double bond]O peptide analogue. By correcting the known inadequacies in the calculations with the average theoretical to experimental ratio from the benchmark molecules of the system, it is possible to obtain a best estimate of rotational constants and infrared frequencies that should be precise enough to initiate laboratory experiments and/or observations. The corrected values of B=6.0342 GHz and C=5.4921 GHz for NH2[bond]CH[double bond]S; B=9.2292 GHz and C=6.1164 GHz for NH2[bond]SiH[double bond]O; B=8.0275 GHz and C=6.4779 GHz for CH3[bond]P[double bond]O should be accurate to within a few tenths of a per cent. Theoretical infrared spectra are also provided to assist in identification of these exotic species.

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